the girl seriously should go have a check up.
For a female to have abnormal menstrual cycles, its killing her chance for healthy fertility. She might have problem being pregnant or have children in future.

Some girls have quarterly mentruals cycle, some only have 4 times in a year... and there are some who have everyday menstrual cycle that only stop one day in a year period. Yes, these are unlucky souls and as their doctor advised, its difficult for them to have children in the future. And they have to take medication as well.